Sounding data often consists of a series of echoes in frequency vs. distance space. Distance is typically derived from the time delay between when a transmitted pulse at a given frequency is sent and an echo is received. The distance value may be scaled by a nominal propagation velocity. When the distance is plotted against frequency the echoes often form traces characterized by cusps. An idealized sounding 10 is shown in FIG. 1, showing two cusps at Fc1 and Fc2.
Often soundings may include multiple traces offset in frequency and/or distance and may include interferences from various sources. Traces may also be incomplete or vary in thickness. A typical raw ionospheric sounding (ionogram) 20 is shown in FIG. 2, showing multiple traces, interference bands and thick traces. Such complications make it difficult to determine trace parameters, such as the critical frequency, and/or distance. The distance coordinate in ionograms is referred to as virtual height. Its relation to the actual or true height of the trace depends on the amount of ionization present.
“Scaling” is the recognition and characterization of traces in a sounding. Traditionally, scaling occurs at some later time after the sounding was performed and is often performed by a trained technician. Modern sounders often incorporate software that attempts to scale the sounding in near-real time, but the quality of the results has been highly variable. In the case of ionospheric soundings, for example, interference and/or multiple echoes lead to misleading results.
Accordingly, there is a need in the art for a system to return accurate distance and frequency estimates for cusps and traces in the sounding data.